P454: VENETOCLAX AND GILTERITINIB SYNERGIZE IN FLT3 WILDTYPE ACUTE MYELOID LEUKEMIA BY SUPPRESSION OF MCL-1 VIA COMBINED AXL AND FLT3 TARGETING
Authors: C. Schmidt, M. Janssen, P.-M. Bruch, M. F. Blank, C. Rohde, A. Waclawiczek, S. Renders, D. Heid, S. Göllner, L. Vierbaum, K. Weidenauer, S. Herbst, M. Knoll, C. Kolb, B. Besenbeck, M. Fabre, M. Gu, R. Schlenk, F. Stölzel, M. Bornhäuser, C. Röllig, U. Platzbecker, C. Baldus, H. Serve, T. Sauer, S. Raffel, C. Pabst, G. Vassiliou, B. Vick, I. Jeremias, A. Trumpp, J. Krijgsveld, C. Müller-Tidow, S. Dietrich
Journal: HemaSphere (2022)

Background: BCL-2 inhibition has been shown to be effective in older patients with acute myeloid leukemia (AML) in combination with hypomethylating agents or low-dose cytarabine. However, treatment resistance and relapse represent major clinical challenges. Thus, there is an unmet need to overcome resistance to current venetoclax-based regimens. Aims: In order to establish an alternative treatment approach for AML in elderly patients, we aimed at identifying a highly synergistic drug combination partner for venetoclax. Methods: We performed a high-throughput drug screening to identify the most effective combination partner for venetoclax in AML. Overall, 64 anti-leukemic drugs were screened in 31 primary high-risk AML samples in the presence or absence of venetoclax. We calculated drug synergies, validated top venetoclax combination partners in AML cell lines and primary patient samples and performed mechanistic analyses. Results: Established anti-leukemic drugs exhibited only weak synergism with venetoclax in high-risk AML samples. In contrast, when targeting distinct pathways such as FLT3 signaling, we observed increased synergistic activity. Gilteritinib exhibited highest synergy with venetoclax in FLT3 wildtype AML, with especially high synergy values in TP53 mutated samples. The combination of gilteritinib and venetoclax increased apoptosis, reduced viability and abolished colony-formation potential in FLT3 wildtype as well as venetoclax-azacitidine resistant cell lines and primary patient samples. Proteomics revealed increased levels for proteins involved in FLT3 wildtype signaling in specimens with low in-vitro response to the currently used venetoclax-azacitidine combination. Mechanistically, venetoclax with gilteritinib decreased phosphorylation of ERK and GSK3B with subsequent suppression of the antiapoptotic protein MCL-1. MCL-1 downregulation was associated with increased MCL-1 phosphorylation of serine 159 and proteasomal degradation. Compared to other FLT3 inhibiting drugs, gilteritinib showed highest synergism with venetoclax due to the additional inhibition of AXL that reinforced the downregulation of MCL-1. Gilteritinib and venetoclax proved efficacious in an FLT3 wildtype PDX model with TP53 mutation. Furthermore, the drug combination reduced leukemic burden in four patients with venetoclax-azacitidine refractory AML, who received gilteritinib and venetoclax as an individual treatment approach. Summary/Conclusion: In summary, our results identified gilteritinib as a potential therapy combination partner for venetoclax in patients with FLT3 wildtype AML.